This invention relates to an actuator having a mobility of two or more degrees of freedom and to a robot mechanism designed to utilize such an actuator. In particular, this invention relates to an actuator which is suitable for use in an automatic subject follow-up device for a video camera and a joint device in a robot.
Conventionally, an actuator having a high degree of freedom, in particular a mobility of a freedom of three degrees or more, such as one used in a robot joint mechanism, has been designed to be supplied with driving forces by two or more pulse motors, as described in No. 533, page 821 to 822 of the collection of treatises in respect of the scientific lectures given at the Spring 1984 Meeting of the Precision Instrument Society. This conventional design involves a complicated device structure and a large size.
In view of this, a small and lightweight actuator was later developed in the form of a system using ring-like piezoelectric motor elements, each of which consists of piezoelectric elements, this being described in Japanese Patent Laid-Open No. 62-141978.
However, since the above conventional actuator utilizes a plurality of ring-like piezoelectric motor elements, the area of the parts thereof that are driven by the piezoelectric elements is quite small in comparison with the contact area between the driving member and the driven member, resulting in a rather weak driving force.